Microtome feed mechanism

ABSTRACT

Microtome feed mechanism which provides the requisite relative motion of the specimen in relation to the sectioning tool at sectioning in a microtome. The feed mechanism comprises a body made of a rheological material arranged between that part of the microtome which is continuously fed and a component which is mainly fixed to the foundation block of the microtome, the mechanism further comprising a force generating means between the fed part and the component fixed to the foundation, from which force generating means the fed part is influenced by a substantially constant force in the feeding direction. Hence a substantially constant feeding rate is obtained due to the deformation of the body made of a rheological material. The mechanism can be arranged in such a way that the body is being compressed, extended, or sheared.

United States Patent Forsstrom [54] MICROTOME FEED MECHANISM [72] inventor: Bo Goeta Forsstrom, Skalby,

Sweden [73] Assignee: LKB-Produkter AB,

Sweden [22] Filed: April 26, 1971 [2]] Appi. N0.: 137,196

Bromma,

[ 30] Foreign Application Priority Data May 8, 1970 Sweden 6344/70 [56] References Cited UNITED STATES PATENTS 2/1971 Burkhardt ..83l9l5.5X [0/197] Wistedt ..83/9i5.5X

[451 Sept. 19, 1972 Primary Examiner-Frank T. Yost Attorney-Christen & Sabol [57] ABSTRACT Microtome feed mechanism which provides the requisite relative motion of the specimen in relation to the sectioning tool at sectioning in a microtome. The feed mechanism comprises a body made of a rheological material arranged between that part of the microtome which is continuously fed and a component which is mainly fixed to the foundation block of the microtome, the mechanism further comprising a force generating means between the fed part and the component fixed to the foundation, from which force generating means the fed part is influenced by a substantially constant force in the feeding direction. Hence a substantially constant feeding rate is obtained due to the deformation of the body made of a rheological material. The mechanism can be arranged in such a way that the body is being compressed, extended, or sheared.

6 Claims, 5 Drawing Figures mcao'rom: man smcnxmsm This invention relates to a mechanism for providing the requisite relative motion of the specimen in relation to the sectioning tool at sectioning in a microtome.

Sectioning of a specimen in a microtome is suitably carried out by means of fixing the specimen in one end of a specimen arm which is moved up and down while the specimen arm is fed at an exceedingly low constant rate so that very thin sections of the specimen, appropriate for examination in an electron microscope, can be obtained by means of a knife, arranged at the end of the specimen arm. If it is desired to obtain sections of a thickness of 500 A and the sectioning frequency must not exceed 25 sectionings per minute, the feeding rate should be in the range of 12,500 A per minute. A generally applied means of providing such a feed consists in slowly heating the specimen arm, e.g. by a coil, wound round the specimen arm. The disadvantage of a procedure like that is that, if the heating continues for an extended period, a nonlinear expansion of the specimen arm is obtained, and furthermore a proportionately long time is required to restore the specimen arm after heating. Hence the intention of the present invention is to provide a feeding device for a microtome, having the disadvantages mentioned above eliminated. The characteristics of the mechanism will appear from the claims following the specification.

The invention will now be further explained with reference to the accompanying drawing in which:

FIG. I schematically shows a microtome, equipped with a feed mechanism according to the invention,

FIG. 2 shows a second embodiment of the feed mechanism according to the invention, and

FIG. 3 shows a third embodiment of the feed mechanism according to the invention, and

FIG. 4 a-b is a diagram showing the extension as a function of time at a constant applied tension for a material utilized in the feed mechanism according to the invention.

In FIG. I, which schematically shows a microtome equipped with a feed mechanism according to the invention, reference 1 denotes the foundation block of the microtome. n the foundation a knife 3 is arranged, attached in a knife stage 2. The knife stage is displaceable along the foundation, e.g. by means of a slide, not shown in the drawing. The foundation is further equipped with a resiliently fastened support 4, which via a plastic body 5 is connected to a feeding arm 6, the arm via a spring blade 7 being connected to the foundation. The feeding arm 6 is, by a spring blade 10, connected to a specimen arm 8, to the end of which a specimen 9 is suitably attached. The specimen arm can be moved up and down by means of a cord 11 con nected to a driving device, not shown in the drawing. A spring 13 is constricted between the feeding arm 6 and an adjusting screw 12, tapped through the support 4, by means of which the spring pressure on the feeding arm 6 can be varied. The foundation 1 is further equipped with an abutment 14 with an adjusting screw 16 tapped through it. By means of the adjusting screw 16 the spring rate of a spring 15, arranged between the screw and the support 4, can be varied. The abutment 14 is further equipped with a magnet 17, with a coil 18 on it. The described device works in the following manner. First a coarse adjustment of the knife in relation to the specimen is made by means of a displacement of the knife stage 2. Then the up and down motion of the specimen arm 8 is started by means of the motor, connected to the cord 11. During the upward motion of the specimen arm the magnet 17 is activated by applying a magnetizing current to the coil 18. The support 4 is thus attracted towards the magnet whereby the specimen 9 is removed from the knife 3 so that this one will not make damage to the specimen at the upward motion. During the sectioning process the plastic body 5 will get deformed under influence of the force of the spring 13 in order that the feeding arm 6 will be displaced at a substantially constant rate. The material of the plastic body, its dimension and the force of the spring 13 are then chosen in such a way that the deforman'on during all the sectioning process occurs in a range where the plastic body has a linear extension curve, whereby a most accurate linear motion of the arm 6 is obtained. The purpose of the adjusting screw 16 and adherent spring 15 is to make possible to achieve a faster feed of the specimen, e.g. if thicker sections are desired for light microscopy. The microtome according to FIG. I is further equipped with an excentric 19 by means of which the feeding arm 6 can be separated from the support 4 in order that the plastic body 5 can be replaced. As the plastic body for recovering of its original form requires a time in the range of 3-5 times the deformation time it is desirable that the body is easily replaceable. The replacement can e.g. be arranged in that way that a number of plastic bodies are arranged in a revolver which after the feeding arm 6 is separated from the support 4 is able to feed a new plastic body.

According to the above feeding device the feeding is thus accomplished by deforming a plastic body. The disadvantages of thermal feeding are in that way eliminated. In the device shown in FIG. 1 the deformation of the plastic body is obtained by applying a pres sure to the plastic body. Analogous results are, however, obtained by applying an elongation strain or a shearing strain to the plastic body as well. Examples of such embodiments of the device according to the invention are shown in FIG. 2 and 3.

In FIG. 2 the feeding arm 6 is thus arranged at that end side of the support 4 which is turning towards the knife, and the plastic body is attached to the support and to the arm. The spring 13 thereby gives raise to elongation strain in the plastic body.

In the device shown in FIG. 3 the arm 6 is arranged beneath the support 4 and the plastic body 5 is fastened between the support and the arm. The spring 13 thereby gives raise to shearing strain in the plastic body. Combinations of devices according to FIGS. 1 2, and 3 are of course pouible as well.

In FIG. 4 a and b the elongation e is shown as a function of time in a plastic body influenced by a force 0-,, which is a constant versus time. When applying a constant strain on a polymer material a deformation is obtained, which is a function time. A creep is thus ob tained. The creep thereby comprises an immediate elongation s which is elastic. Then a delayed elastic elongation is obtained in accordance with the exponential curve, indicated to the left in FIG. 4 b, the first part of which can be approximated into a straight line. The viscous elastic elongation changes for certain plastic materials at a time I. into a viscous flow which is mainly linear versus time. in the feeding device according to the present invention the viscous elastic range is suitably utilized, in which the deformation is reversible and in the first part of which the exponential curve can be approximated into a straight line. In the above feeding device a displacement of the arm 6 of about 0.1 mm within l minutes is desired. A suitable magnitude of the force from the spring 13 is 5 kp. Examples of materials which under the above mentioned conditions can be dimensioned so that a mainly linear viscous elastic elongation is obtained are softened epoxy resins.

It should also be pointed out that by suitable compensating measures it is possible to achieve an elongation curve which very closely follows a straight line in the viscous elastic range. If, e.g., .,the pressure or the temperature is successively reduced the bend of the curve will decrease. The compensation can also be accomplished by compounding the plastic body of a number of different materials which give a resulting elongation curve which is closely linear. As evident from FIG. 4 b there is a plateau in the elongation curve after the viscous elastic elongation, the plateau being followed by a linear elongation. This is due to that some plastic materials after a certain period of time begin to flow which gives raise to allinear elongation. Of course it is also possible in the feeding device according to the invention to utilize this part of the curve. The disadvantage, however, is that the flow is irreversible. It will also be perceived that the material which is deformed in the feeding process not necessarily is a plastic material. In principle any material, the elongation of which is a function of time, a so called rheological material, can of course be used. It is e.g. possible to utilize a clay material.

Finally it should be stated that the device described above only represents one embodiment of the invention. Of course several embodiments are possible within the scope of the following claims. Thus the relative motion between the specimen and the knife can of course also be accomplished in that way that the knife is fed.

We claim:

I. Mechanism for providing the relative motion of the specimen in relation to the sectioning tool, requisite at sectioning in a microtome, characterized in that it comprises a body (5) made of a rheological material, which is arranged between that part (6) of the microtome which is continuously fed in the relative motion and a component (4) which is mainly fixed to the foundation, the mechanism further comprising a force generating means (13) between the fed part and the component fixed to the foundation, from which force generating component the fed part is influenced by a substantially constant force in the feeding direction, so that a substantially constant feeding rate is obtained due to the deformation of the body.

2. Mechanism according to claim 1, characterized in that the fed part (6) and the component (4) fixed to the foundation are mutually arranged in that way that the body (5) will be compressed by the force generating means (13).

3. Mechanism according to claim 1, characterized in that the fed part (6) and the component (4) fixed to the 4. Mechanism according to claim 1, characterized in that the fed part (6) and the component (4) fixed to the foundation are mutually arranged in such a way that the body (5) is sheared by he force generating means 

1. Mechanism for providing the relative motion of the specimen in relation to the sectioning tool, requisite at sectioning in a microtome, characterized in that it comprises a body (5) made of a rheological material, which is arranged between that part (6) of the microtome which is continuously fed in the relative motion and a component (4) which is mainly fixed to the foundation, the mechanism further comprising a force generating means (13) between the fed part and the component fixed to the foundation, from which force generating component the fed part is influenced by a substantially constant force in the feeding direction, so that a substantially constant feeding rate is obtained due to the deformation of the body.
 2. Mechanism according to claim 1, characterized in that the fed part (6) and the component (4) fixed to the foundation are mutually arranged in that way that the body (5) will be compressed by the force generating means (13).
 3. Mechanism according to claim 1, characterized in that the fed part (6) and the component (4) fixed to the foundation are mutually arranged in such a way that the body (5) is extended by the force generating means (13).
 4. Mechanism according to claim 1, characterized in that the fed part (6) and the component (4) fixed to the foundation are mutually arranged in such a way that the body (5) is sheared by he force generating means (13).
 5. Mechanism according to claim 1, characterized in that the fed part (6) constitutes a feeding arm, mechanically connected to the specimen arm (8).
 6. Mechanism according to claim 1, characterized in that the foRce generating means (13) consists of a spring. 